Sperm-Associated Antigen 16 Is a Novel Target of the Humoral Autoimmune Response in Multiple Sclerosis

We have previously identified eight novel autoantibody targets in the cerebrospinal fluid of multiple sclerosis (MS) patients, including sperm-associated Ag 16 (SPAG16). In the current study, we further investigated the autoantibody response against SPAG16-a protein with unknown function in the CNS-and its expression in MS pathology. Using isoelectric focusing, we detected SPAG16-specific oligoclonal bands in the cerebrospinal fluid of 5 of 23 MS patients (22%). Analysis of the anti-SPAG16 Ab reactivity in the plasma of a total of 531 donors using ELISA demonstrated significantly elevated anti-SPAG16 Ab levels (p = 0.002) in 32 of 153 MS patients (21%) compared with all other control groups with 95% specificity for the disease. To investigate the pathologic relevance of anti-SPAG16 Abs in vivo, anti-SPAG16 Abs were injected in mice with experimental autoimmune encephalomyelitis, resulting in a significant disease exacerbation. Finally, we demonstrated a consistent upregulation of SPAG16 in MS brain and experimental autoimmune encephalomyelitis spinal cord lesions, more specifically in reactive astrocytes. We conclude that SPAG16 is a novel autoantibody target in a subgroup of MS patients and in combination with other diagnostic criteria, elevated levels of anti-SPAG16 Abs could be used as a biomarker for diagnosis. Furthermore, the pathologic relevance of anti-SPAG16 Abs was shown in vivo.